Hot cathode electron discharge tube



July 11, 1933. H. M. FREEMAN ET AL HOT CATHODE ELECTRON DISCHARGE TUBEOriginal Filed Jan. 1925 5/35 'T' INVENTO R5 f/uer/ /7 fieeman 3WITNESSES [xx/W fifii-MAM Wa//a:e 6 Node.

ATTORNEY Patented July 11, 1933 UNITED STATES PATENT OFFICE HUBERT M.FREEMAN, OF EAST P ITTSBUBGH, PENNSYLVANIA, AND WALLACE G.

WADE, OF NEW YORK, N. Y., ASSIGNORS TO WESTINGHOUSE ELECTBIC- AND MANU-FACTURING COMPANY, A CORPORATION OF PENNSYLVANIA HOT CATHODE ELECTRONDISCHARGE TUBE Original application filed January 8, 1923, Serial No611,263. Divided and this application filed July 8,

1926. Serial No. 120,579. Renewed April 24, 1931.

; ending application, erial No. 611,263, filed an. 8, 1923 and of whichthis application is a division.

The principal object of the present invention is to provide an improvedcathode structure for electron discharge tubes, in

which alternating current is utilized to heat the cathode to atemperature at which it emits electrons.

Another object of our invention is to provide a simple cathode structureof the above described character and having good mechanical qualities soarranged as to eliminate as much as possible the undesirable effects ofthe pulsations of the heating current on the flow of the electrons fromthe cathode without impairing the high cathode eficiency.

A cathode construction constituting a preferred embodiment of theinvention, comprises two tubular refractory members disposed inside-by-side relation and having therearound a wrapping or coating ofconducting material adapted to emit electrons when heated. A hairpinshaped heater wire has its two sides threaded through the perforationsof the two refractory tubes and is arranged to be supplied byalternating current for heating the refractory members and the electronemitting material on the surface thereof.

The foregoing construction permits very close spacing between the twowires of the hairpin-shaped heater element, thus reducing the magneticfield produced by the alternating heating current to a minimum andeliminating the undesirable influence that such currents may have on theflow of electrons from the electron emitting surface of the cathode. Atthe same time, the improved construction utilizes a minimum ofrefractory material requiring little time for heating it, and theelectron emitting surface material thereof, to the desired operatingtemperature. The improved structure has also the further advantage thatit gives a relatively large emitting surface with a minimum amount ofmaterial.

Our invention will be best understood from the accompanying drawing, inwhich Figure 1 is a view partially in elevation and partially in sectionof a radio tube embodying the invention, with a diagrammatic view of thecircuits associated therewith,

Fi 2 is a horizontal sectional view along the line IIII of the cathodestructure of the tube shown in Fig. 1,

Fig. 3 is an elevational view of a modified catiode structure embodyingour invention, an

Fig. 4 is a horizontal enlar ed sectional view of the cathode structures own in Fig. 3, along the line IVIV.

Referring to Fig. 1, a radio receiving tube embodying the invention isshown comprising an elongated, suitably evacuated envelope 2, having areentrant stem 3, terminating in a press 4. Five leading-in wires 6 to10, are fused into the press and serve to support, and to makeconnections to, a cathode structure 12 and concentrically mounted gridand anode structures 13 and 14:.

The cathode structure 12, which constitutes the distinct feature of theinvention, comprises two tubular members 15 and 16, in the shape ofslender solid cylinders of refractory material, disposed in side-by-siderelation and having longitudinal, central perforations 17. A heaterelement or wire 21, which is bent in the shape of a hairpin, is threadedthrough the two perforations 17 the two sides or sections 22 of theheater element being insulatingly spaced from each other by the walls ofthe refractory cylinders 15 and 16, which thus constitute a refractorybody in which the heater element is completely embedded. The thicknessof the walls of the refractory cylinders is made as small as isfeasible, in order to reduce the spacing between the parallel sides 22,of the heater element, to a minimum. Such construction has been found tosubstantially eliminate the fluctuating magnetic field that wouldotherwise be established by the alternating current with which thisheater wire is being supplied.

The two tubular members 15 and 16 are made of an insulating refractorymaterial, which does not chemically or otherwise react with the heaterelement embedded therein. Zircon has been found very suitable for thisurpose.

The cathode element proper, from which the electron flow in the tube isobtained, consists of a wrapping 25 of conducting mate rial, surroundingthe two refractory members 15 and 16. In the form of our invention shownin Figs. 1 and 2, the wrapping 25 is formed by helically winding anoxide coated platinum strip around the outer surfaces of the tworefractory cylinders, the platinum strip being heated to the electronemitting temperature-through the medium of the refractory bodies, whichthus perform the double function of insulating the electron emittingcathode surface from the alternating-current energized heating element,and, at the same time, conveying thereto the heat generated inside theheating element.

The oxide coating on the platinum strip 25, which is utilized as thecathode surface, may be made in any of the familiar ways. Very goodresults are obtained when a coating of the oxides of barium, strontiumor the like is used.

The cathode structure consists thus of a tubular envelope or sheath,surrounding a pair of heating wires and insulatingly spaced therefrom byan elongated heater body which surrounds the heater wires, the cathodesheath conforming in its outer con tour to the shape of the heaterelement. The cathode element itself has the shape of a flattened tubularmember of oblong cross section corresponding to the shape of the bodyconstituted by the two adjacently disposed refractory heater elements.

The above-described cathode structure may be supported by means of acarrier rod 26 extending from the lead-in wire 6 and holding the bentportion of the heater wire 21 at its upper end.. The electron emittingwrapping 25 has a suitable electrical connection to the carrier rod 26,which also serves as an external terminal connection to the cathodesurface.

The lower end of the cathode structure 12 is held in place by theleadein wires 7 and 8, which are welded to the lower ends of the heaterwire 15 to make electrical connection thereto. The tube is provided with-a suitable base having five contact pins 28, which are connected to thefive lead-in wires 6 to 10 in the usual manner. The improved tube a maybe utilized in any of the familiar circuits, the principal distinctionbeing the means for heating the cathode to maintain the surface thereofat an electron emitting condition.

Inplace of the ordinary storage batteries,

or direct-current sources, which are required in the prior art tubes forheating the cathode, alternating current may be utilized with the tubesmade according to the invention, the two terminals 7 and 8 of the heaterwire 21 being shown connected to a source of alternating current in theform of a transformer 31. The remainder of the circuit in which the tubeis shown to be utilized, comprises input leads, in the form ofconductors 32 and 33 connected to the grid 13 and the cathode element25, respectively, the output circuit of the tube comprising a detectingor'other load device 34 connected in series with a source of plateenergy 35 between the anode 14 and the cathode 25 of the tube.

In Figs. 3 and 4 is shown a cathode construction embodying amodification of the invention in which more direct transmission of heatfrom the heater element 21 to the electron emitting cathode surface issecured. To this end the tubular cathode element 36 is placedsubstantially in direct contact with the heater wires 22 of the heaterelement, being insulated therefrom either by an insulating oxide coating37 covering the interior surface of the tubular cathod element 36, or asimilar coating 38 on the surface of the heater wires 22, or byinsulating coatings on both. The tubular cathode element 31 may be madeby wrapping an oxide coated platinum strip around the two wires 22 ofthe heater element or in any other suitable manner. The finished cathodestructure has the shape of an elongated flat tubular member, the outersurfaces of which is adapted to give large electron emission. Theinsulating coating 38 on the heater wires 22 may comprise magnesiumoxide, or a similar substance.

Tubes embodying cathode constructions of the type described hereinabove,and distinguished by the features more particularly pointed out in theappended claims, have proved very efiicient and it is desired that theappended claims be accorded a broad construction commensurate with theinvention disclosed in the application.

IVe claim as our invention:

1. In a thermionic device, a discharge tube having a cathode structurecomprising a plurality of heater Wire sections arranged in a row,refractory means surrounding said sections and conforming substantiallyto the shape of the envelope of said row, and electron emitting means onthe surface of said refractory means. a

2. In a thermionic device comprising a hot-cathode electron dischargetube, a cat11- odc member in said tube comprising elongated refractoryinsulating means, a pair of substantially parallel heater wire sectionsembedded in said refractory member, said refractory member having anoblong cross alternating heating current thereto, a re fractorysubstantially insulating means surrounding the sides ofsaid heater wireand holding the same inspaced relation, said .means constituting anelongated body having an oblong cross section in a plane perpendicularto the wire sides, an electronemittin sheath surrounding the surface ofsaid refi'actory body and conforming to the shape thereof, and aterminal connection to said sheath.

4. In a hot-cathode electron-discharge tube, a cathode structurecomprisinga pair of parallel disposed heater wire sections havingterminals for conveying current thereto, and an electron-emitting sheathsurrounding said -wires and heated thereby, said sheath constituting anelongated tubular body having flattened side surfaces substantiallyparallel to the plane of said Wires.

5. In a hot-cathode electron-discharge tube, a cathode structurecomprising a tubular elongated member having an electronemittingconducting cathode surface, said member having flattened sides, andheating means in the interior of said member and substantially insulatedfrom the adjacent portions thereof.

6. In a hot-cathode electron-discharge tube, a cathode member comprisinga tubular elongated member having an electronemitting conducting cathodesurface, said member having an oblong cross section, an insulatingmaterial inthe interior of said member a heater element insulatinglyembedded in said material, terminal connections for said heatingelement, and an independent terminal connection for said cathodesurface.

7. In a hot-cathode electron-discharge tube, a cathode structurecomprising a tubular elongated member having an electronernittingconducting cathode surface, said member'having an oblong cross section,an insulating material in the interior of said member, a pair ofserially connected wire sections constituting a hair-pin shaped heatingelement insulatingly embedded in said material, terminal connections forsaid heating element and an independent terminal connection for saidcathode surface.

8. In a hot-cathode electron-discharge tube, a cathode structurecomprising an elongated refractory insulating "member electricalheating-means embedded in the in-- terior of said member and a wrappingof conducting material on the surface of said member, said wrappinghaving an electron emitting terminal connection.

9. In -a hot-cathode electron-discharge tube, a cathode structurecomprising a pluralit of elongated members of substantially insu atingrefractory material disposed in side-b -side relation, astrip ofconducting material tightly wrappedaround said members and constitutingan electron emitting cathode surface, and means embedded within saidrefractory members for heating the same.

10. In a hot-cathode electron-discharge tube, a cathode structurecomprising two parallel disposed heating wire sections, tubularrefractory insulating members surrounding said wires and spacing thesame from each other, a conducting wrapping tying said tubular memberstogether, said wrapping having a surface that emits large quantities ofelectrons when heated.

11. In a thermionic device, a discharge tube having a cathode structurecomprisin a plurality of heater-wire sections arrange in a row,refractory means surrounding, but mechanically separate from, saidsections and conforming substantially to the shape of the envelope ofsaid row, and electronemitting means on the surface of said refractorymeans.

12. An electron-discharge tube, comprising a cathode structurecomprising an elec trically conducting heat-ing element, an electricallyconducting strip having an electronemitting surface wound about andsupported by said heating element and electrically insulated therefromexcept that said strip is connected to said heating element atsubstantially the mid-point of said heating element.

13. A thermionic cathode electron-discharge tube comprising a cathodestructure comprising a U-shape heating wire havin closely disposedparallel heater sections an a tubular sheath of conducting materialembracing said heater sections, such sheath comprising a helix ofconducting material wound around said sections, the outer surface ofsaid helix having a coating of electron-emitting oxides.

14. An electron discharge tube, comprising a cathode structurecomprising an electrically conducting heating element, an electricallyconducting strip having an electronemitting surface wound about andsupportcharge tube comprising a cathode structure comprising a U-shapeheating wire having closely disposed parallel heater sections havcathodemember having a continuous outer surface adapted to emit electrons whenheated, a U-shape heater wire longitudinally disposed in said tubularcasing and refractory tubular members individually surrounding the sidesof said heater members for insulating the same with respect to eachother and to the Walls of said outer casing.

In testimony whereof, we have hereunto subscribed our names this 26thday of June, 1926, and this 23rd day of June, 1926, respectively.

HUBERT M. FREEMAN. WALLACE G. WADE.

